Re: Predicate Locks for writes?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Predicate Locks for writes?
Date: 2017-10-11 14:33:32
Message-ID: CA+TgmobboJhp-tGHnTQiOcraOMMP=ZK7k+AX+pLCnaK1ZoYvyA@mail.gmail.com
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On Sat, Oct 7, 2017 at 7:26 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> PredicateLockTuple() specifically avoids adding an SIRead lock if the
> tuple already has a write lock on it, so surely it must also be
> correct to skip the SIRead lock if we are just about to update the
> row?

I wonder if there's a race condition. Can someone else read/update
the tuple between the time when we would've taken the SIRead lock and
the time when we would have gotten the actual tuple lock?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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